Dipeptidyl peptidase (DPP)-4 and neprilysin (NEP) rapidly degrade glucagon-like peptide 1 (GLP-1) in mice. Commercially available sandwich ELISA kits may not accurately detect the degradation products, leading to potentially misleading results. We aimed to stabilize GLP-1 in mice allowing reliable measurement with sensitive commercially available ELISA kits. Non-anesthetized male C57Bl/6JRj mice were subjected to an oral glucose tolerance test (OGTT; 2 g/kg glucose), and plasma total and intact GLP-1 were measured (Mercodia and Alpco ELISA kits, respectively). No GLP-1 increases were seen in samples taken beyond 15 minutes after the glucose load. Samples taken at 5 and 10 minutes after the OGTT showed a minor increase in total, but not intact GLP-1. We then administered saline (control), or a DPP-4 inhibitor (valine pyrrolidide or sitagliptin) with or without a NEP-inhibitor (sacubitril) 30 minutes before the OGTT. In the inhibitor groups only, intact GLP-1 increased significantly during the OGTT. After injecting male C57Bl/6JRj mice with a known dose of GLP-1(7-36)NH2, peak GLP-1 levels were barely detectable after saline, but 5-10-fold higher during sitagliptin and the combination of sitagliptin/sacubitril. The half-life of the GLP-1 plasma disappearance increased up to 7-fold during inhibitor treatment. We conclude that reliable measurement of GLP-1 secretion is not possible in mice in vivo with commercially available sandwich ELISA kits, unless degradation is prevented by inhibition of DPP-4 and perhaps neprilysin. The described approach allows improved estimates of GLP-1 secretion for future studies, although it is a limitation that these inhibitors additionally influence levels of insulin and glucagon.

中文翻译：

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体内抑制二肽基肽酶 4 可测量小鼠 GLP-1 分泌

二肽基肽酶 (DPP)-4 和脑啡肽酶 (NEP) 可快速降解小鼠体内的胰高血糖素样肽 1 (GLP-1)。市售的夹心 ELISA 试剂盒可能无法准确检测降解产物，从而导致潜在的误导性结果。我们的目标是稳定小鼠体内的 GLP-1，从而能够使用敏感的市售 ELISA 试剂盒进行可靠的测量。对未麻醉的雄性 C57Bl/6JRj 小鼠进行口服葡萄糖耐量试验（OGTT；2 g/kg 葡萄糖），并测量血浆总 GLP-1 和完整 GLP-1（分别为 Mercodia 和 Alpco ELISA 试剂盒）。葡萄糖负荷后 15 分钟后采集的样本中未发现 GLP-1 增加。 OGTT 后 5 分钟和 10 分钟采集的样本显示 GLP-1 总量略有增加，但并非完整。然后，我们在 OGTT 前 30 分钟给予生理盐水（对照）或 DPP-4 抑制剂（缬氨酸吡咯烷或西他列汀）联合或不联合 NEP 抑制剂（沙库巴曲）。仅在抑制剂组中，完整 GLP-1 在 OGTT 期间显着增加。给雄性 C57Bl/6JRj 小鼠注射已知剂量的 GLP-1(7-36)NH2 后，在盐水中几乎检测不到峰值 GLP-1 水平，但在西他列汀和西他列汀/沙库巴曲组合期间高出 5-10 倍。在抑制剂治疗期间，GLP-1 血浆消失的半衰期增加了 7 倍。我们的结论是，使用市售的夹心 ELISA 试剂盒不可能在小鼠体内可靠地测量 GLP-1 分泌，除非通过抑制 DPP-4 和脑啡肽酶来防止降解。所描述的方法可以改进对未来研究的 GLP-1 分泌的估计，尽管这些抑制剂另外影响胰岛素和胰高血糖素的水平是一个限制。